The DNT is a device that connects to your cell phone and then ties in with either a single phone in your house or your house's phone wiring. If tied in to the house's wiring, it must be on a line that does not have telephone company (TelCo) service. In my case, although I no longer have regular phone service, I have a DSL broadband connection coming in from TelCo on Line 1 (L1). I hooked up the system to L1 and it allowed me to make outgoing calls but it would not connect to incoming. Since this kind of trouble was not unexpected I immediately yielded and switched over to Line 2 (L2). On the DNT, this is as easy as flipping a switch. However, without an L2 capable phone, provision must be made to bring the L2 (outer two) conductors of the phone cord connector to the center (inner two) lines so the L1 only phones can "talk" on L2. I installed an L1/L2 capable phone on the kitchen wall and used an idle L1 to L2 "Two-Line Splitter" (Radio Shack part number 279-432) adapter to connect my Panasonic KX-TG8231 phone base to L2 and everything worked ... yours truly was quite happy.
Of course, happiness can be very fleeting and, in this case, I remembered that I still had an older "Trimline" phone in the basement that I wanted to continue using. To avoid a severe case of "engineering unhappiness" I decided I needed to make a trip to Radio Shack for another "Two-Line Splitter". Alas, more unhappiness awaited me there as I found out that this simple little device appears to be what Radio Shack is trying to use to carry it through these tough economic times. They charged me $8.47 (tax included) for this thing ... and I reluctantly paid it and made my way home. On the way, however, the engineering mindset quickly took over, attempting to steer me back to Nirvana. It occurred to me that I might be able to fashion a simple Line 2 to Line 1 swap cable out of home telephone wiring supplies I already had. My supplies on hand comprised a standard RJ-11 stripping/crimping tool, RJ-11 connectors and flat 4-conductor phone cable (all purchased long ago at Menards).
The process is pretty straightforward, as outlined below. As usual, though, the devil is in the details, so let's first go over a little introductory information on the standard RJ-11 connector and home telephone wiring. The RJ-11 connector form factor has six pins and so it can handle up to 6 conductors. Typical home operation uses only 2 or 4 of those conductors. The RJ-11 connector pins have a numbering scheme that will be useful in the discussion below. Holding one up with the connector tab facing away from you and the "business end" of the connector facing up, the pins are numbered 1-6 from left to right.
We will be discussing a common home wiring scheme that uses 4 conductors located in pins 2 through 5 (the outer 2 pins, 1 and 6, are unused) and flat 4-conductor cable with conductor insulation colors of Black, Red, Green and Yellow. Note that more recent telephone wiring that you may buy may use a different conductor color scheme, typically as follows: Black becomes White with an Orange stripe, Red is now Blue with a White stripe, Green becomes White with a Blue stripe and Yellow is now Orange with a White stripe. But regardless of the color scheme of the wiring you use, just translate as necessary (and be consistent throughout) as I will use the "old" (Black, Red, Green, Yellow) colors in this writeup.
In a typical home phone wiring installation, Line 1 (L1) is run through the center two conductors of the RJ-11 connector. These are the Red and Green conductors located on pins 3 and 4. Similarly, Line 2 (L2) is connected through the next most outer pair, pins 2 and 5, using the Black and Yellow colored conductors. The outside 2 pins, 1 and 6, as mentioned earlier, are typically not used. With this background in mind, our goal is to take the Line 2 connection at the wall jack (pins 2 and 5) and make it come out of the Line 1 pins (3 and 4) of the RJ-11 connector at the phone end of our swap cable. Let's look at the details of one way to accomplish this:
Supplies needed: Standard RJ-11 stripping/crimping tool, at least 2 RJ-11 connectors that accept 4 conductor flat cable and a length (as needed for your specific project) of flat, 4 conductor telephone cable.
Detailed steps:
1. Use the stripping/crimping tool's outer insulation stripper twice to obtain about 1/2" of stripped flat telephone cord on one end (i.e., there will be about 1/2" of the 4 conductor wires showing, and note that the individual conductor wire insulation, colored Black, Red, Green, Yellow, is still in place). For discussion purposes here, this is the end that will plug in to the telephone and we'll call it "L2" (since the two center connectors will have become the Black and Yellow "Line 2" conductors, instead of the normal Red and Green "Line 1" conductors, when we're through).
2. Strip the other end to the normal length (1/4") as defined by the tool. This is the end that will plug in to the wall jack and we'll identify it here as the "L1/L2" end (since the two center conductors, Green and Red, will have the L1 signal and the two outer conductors, Yellow and Black, will have the L2 signal ... note that this is a standard RJ-11 wiring convention).
3. Addressing the L2 (more complex) end of the wire first, carefully twist the Yellow/Green pair together so that Yellow conductor ends up in the center. Then twist the Red/Black pair so that Black similarly ends up in the center right next to Yellow. Looking at the 4 wires, you should now have them laid out as Red, Black, Yellow, Green (or Green, Yellow, Black, Red if you're looking at it from the other side).
4. Hold the wires so that they are parallel at the ends and insert them into an RJ-11 4 wire connector (6 wire connectors work too, just be sure to leave the outer two slots in the connector open). The conductor/connector pin relationship should be as follows: Pin 2-Red, Pin 3-Black, Pin 4-Yellow, Pin 5-Green (see Photo above). I found that it was easy for them to "untwist" during the insertion process and I had to redo this a few times to get it right. Another hint that might help is that I noticed some of the leads (for example, the Black wire in the Photo above) were a little longer than others so, just before inserting them into the connector, I made a single cut across the ends to make them all "just right" with a total length (from the end of the flat insulation) of just under 7/16". This seems to be very good for the crimping process but you might be able to shorten it up even more to, say, 5/16" as this would put the flat insulation a little further into the connector, which seems like a good idea. A caution, though, to not trim the conductor wire ends until you have successfully gotten the wires twisted together as it's much more difficult to do that with shorter conductors.
5. Before crimping the connector onto the wires, check carefully (one more time) to be sure that the Black and Yellow conductors are in the two center pins and the Red and Green conductors are in the two outer pins, as described in step 4. We don't really care about the Green and Red conductors but if done as described here, you should also find that L1 from the wall jack is interpreted as L2 at the "phone" end of the cable (just like the Line 2 wires from the wall jack are connected to the Line 1 pins at the "phone" end ... which is our goal). When you're satisfied, use the tool to crimp the connector in place.
6. Addressing the wall jack end of the cable (per #2, above, we're calling it the "L1/L2" end), note first that the connector can be put on the cable in either of two ways. But only one of those two ways is correct. Based on our understanding of the pin numbering scheme of the RJ-11 connector (see introductory material and the first photo, above), the conductor/pin relationship at this end of the cable should be as follows: Pin 2-Yellow, Pin 3-Green, Pin 4-Red, Pin 5-Black. Double check that this is the case (again, remember the old adage, "measure twice, cut once") and, finally, crimp the L1/L2 connector and you're done!
7. To test your new "Wall Jack Line 2" to "Phone Line 1" swap cable, plug it in to the wall and the phone and see if it works as expected. Note that the cable can, in fact, be plugged in either way ... the identification of "wall jack" and "phone" cable ends, above, was done only to facilitate the fabrication process while noting that the "L1/L2" end is the "simple" end of the cable and the "L2" end is the more complex. So if, when you've completed your project, the cable is not right (i.e., your phone test fails), just cut off the offending L1/L2 connector (the simple end) and put a new one on with the opposite orientation with respect to the 4 conductors. This will work if the L2 end was properly built, so if it doesn't work you will probably have to redo the L2 connector. In my case, the 5' cable worked first time (total cost, about $1.65). One final step I took was to use a fine point Sharpie to label the cable "L1-L2 Swap" so I wouldn't confuse it with any other phone cords and so I wouldn't be tempted to cannibalize it for another application. Here's a photo of the finished cable ends:
Using nomenclature from the above description, the L2 end is on the left and the L1/L2 end is on the right.
Now getting back to the DNT, the setup for my cell phone (Nokia 6085) is to synchronize it with the DNT via Bluetooth and then just leave the phone sitting a few feet away. With my new L1-L2 swap cable installed on the basement Trimline phone, every phone in the house can be used for phone calls using the cell phone connection. The DNT handles the interface to the cell phone and supplies dial tone to the rest of the house phones through the local wiring. When a call comes in to the cell phone, all the phones in the house (including the cell phone, if the ringer is active) ring and I can pick it up on any of them. Also, the CallerID is passed along so it appears on whatever devices have the capability to display it.
The DNT will coexist with a second land line phone system as well. So one could have a land line connection on Line 1 and still use Line 2 for the DNT with a cell phone. As you can imagine, this almost cries out for the phones in the house to be capable of 2-line operation ... but it's still nice to know that it would work (might be a great thing for a home business).
Drawbacks of going all cellular:
1. 911 does not have an automatic "go to" address and GPS may not work indoors
2. Burglar alarm systems typically require a "tip & ring" land line connection (and even if you could get one that worked with the DNT/Cell phone hookup, you'd have to leave a cell phone at home, turned on, just to support the Burglar alarm ... I'd say just get/keep a land line in this case).
3. Cell connection is a bit more noisy than a good land line
4. Fax will not work with cell phone connections and DNT
5. Devices like "Dock-N-Talk" are not free
Positives:
1. Cheaper (saves $25-30/month for same features in Qwest land line)
2. No loss of phone features/use at home, even voice dialing works from extensions in the house
3. Payback on Dock-N-Talk is less than a year, then 100% savings on land line cost
4. To turn off all phones in the house just turn off the cell phone
5. "Feels" good ... and you may even learn how to make an L1-L2 swap cable
Let me know if you have any questions about making this work for you. And tomorrow I need to return my "Two-Line Splitter" to Radio Shack ... ahhh, Nirvana.
